The instant invention relates to vehicle passenger restraint systems and, more specifically, to a firing circuit for an air bag passive restraint system which can be readily diagnosed for the presence of faults therein.
Known air bag passenger restraint systems comprise a firing circuit having a voltage supply providing a potential across a firing squib in series with a first and second normally open vehicle acceleration sensor, each of which is shunted by a resistor of like nominal resistance. A small current thus flows through the circuit while the sensors remain in the normally open condition. The closure of the sensors upon collision or marked deceleration of the vehicle generates a significant rise in the current flowing through the squib which, in turn, fires the squib to deploy the air bag.
In U.S. Pat. No. 4,851,705 issued July 25, 1989, we teach a firing circuit for a passenger restraint system featuring redundant "crash" and "safing" sensors and full fault diagnosability, and its teachings are hereby incorporated herein by reference. Specifically, the '705 patent teaches a firing circuit wherein the simultaneous closure of either of two crash sensors and either of two safing sensors will fire one or more squibs to deploy a like number of air bags. The marketplace has since demanded a firing circuit for a vehicle passenger restraint system featuring a third crash or "discriminating" sensor in addition to the multiple firing paths and full fault diagnosability as taught in the '705 patent.